Due to advances in tunnel building technology, the number of tunnels is increased, and a tunnel is longer. As a tunnel is longer, it is more difficult to circulate air, and density of soot and smoke, contaminants and tiny dust generated by vehicles is higher.
The inside of a tunnel is lower in air density than the outside, and a convection phenomenon does not occur normally, so that air, pollution inside a tunnel is severe.
As a result of investing air pollution inside a tunnel, it turns out that air pollution inside a tunnel is so severe that impurities such as tiny dust (PM10), carbon dioxide, and volatile organic chemicals exceed maximum five times of a reference value. In particular, in case of tiny dust (PM10), about 139 μl/m is detected, which is much higher than the other noxious substances.
Tiny dust means dust having an aerodynamic diameter of less than 10 μm and causes a serious problem to a human body when continuously inhaling them.
Also, air pollution and impurities inside a tunnel makes it difficult for a driver to secure a visual field and to keep a safe following distance, leading to the high incidence of accidents and causing respiratory illness to a driver's respiratory organ.
Polluted air inside a tunnel is exhausted to a residential district around a tunnel to pollute crops or soil, thereby causing huge damage.
In order to prevent air inside a tunnel from being polluted, it is necessary to install a dust collecting means in a tunnel to clean air to be exhausted from a tunnel.
However, as shown in FIG. 1, a high speed tunnel fan 20 is installed in a tunnel to drive air inside a tunnel to be exhausted to the outside of a tunnel, but there is no method for cleaning air to be exhausted from the high speed tunnel fan 20.
As a dust collecting means, an electrostatic precipitating means with a relatively simple structure and high dust collecting efficiency may be attached to a high speed tunnel fan, but there occur several problems in using the existing electrostatic precipitating means.
Firstly, in case of gas which passes through the electrostatic precipitating means at a high speed, whenever an air flow rate is increased by 1 m/s at a limit air flow rate of the electrostatic precipitating means, dust collecting efficiency is lowered by about 5˜10%, whereby dust collecting efficiency is low.
Secondly, a charging portion of the electrostatic precipitating means typically uses a wire method or a saw method, but since a reaction structure area is small when gas flows at a high speed, there is a restriction to charging polluted dust or particles, whereby it can not keep dust collecting efficiency high.
Lastly, a collecting portion for collecting dust or particles is made of alternate plate or stainless plate, but alternate plate or stainless plate has a restriction to collecting and storing polluted dust or particles, do not have constant distribution in generating an electrostatic induction voltage, and has low efficiency since power consumption is high due to an inefficient voltage use.
Therefore, in order to collect polluted dust or particles by using a collecting portion of a plate type, a large number of plate structures are required.
For these reasons, it is impossible to attach the electrostatic precipitating means to the high speed tunnel fan.